P2X receptors (P2XRs) are a distinct family of ligand-gated ion channels that are widely found throughout the peripheral and central nervous system. Recently, we and others have shown that P2XRs are sensitive to the action of ethanol. However, there is a paucity of information regarding the sites of ethanol action on P2XRs. To begin to address this issue, our laboratory has exploited subtype specific differences between P2X2 and P2X3Rs utilizing a chimeric strategy and we have identified regions of the ectodomain that are important for the action of ethanol in P2X3Rs. I propose to extend this line of investigation to P2X4Rs. P2X4Rs are widely distributed in the CNS and have been shown to be inhibited by ethanol. I propose the following Specific Aim: To identify amino acid residues and/or regions on the ectodomain of P2X4Rs that are important for the action of ethanol. This Aim will be accomplished in three steps. Step 1:1 will use two electrode voltage clamp technique and Xenopus oocyte expression system to identify regions on the ectodomain of P2X4Rs important for the action of ethanol. My proposed studies will utilize site-directed mutagenesis and alanine scanning of the ectodomain regions near the TM domains of P2X4Rs to identify key amino acids involved in ethanol's action. Step 2: Extends the investigation of key sites of ethanol action to a mammalian expression system (HEK293 cells). Investigations proposed in this portion of my proposal will test wildtype and mutant P2X4Rs identified in Step 1 using whole-cell patch clamp electrophysiology. Step 2 represents a significant training portion of my proposal. I will learn whole-cell patch-clamp electrophysiology as well as advance cell culture techniques. Step 3:1 will investigate the effects of ethanol on dissociated hippocampal neurons transfected with wildtype or key P2X4R mutants identified in Steps 1 and 2 using whole-cell patch clamp electrophysiology. Over the course of the investigations I will gain valuable new training and expertise in whole cell patch clamp electrophysiology and cell culture techniques. This training will significantly increase my knowledge and ability to continue in the investigation of the role of P2XRs in the action of ethanol as an alcohol researcher in the academic setting. The proposed work will contribute foundation information that will lead to initial molecular models of sites of action for ethanol in P2XRs. The long range goal of this work will be to utilize this knowledge to construct knock-in mice as well as the more conventional knock-out mice to help determine the role specific P2XRs play in mediating behavioral effects of ethanol and if warranted to identify novel therapeutic targets for the treatment of alcoholism.